Fluids, whether they be gaseous or liquid, are typically distributed through a series of conduits which make up a conduit system. In many instances, it is desirable to make a repair or a replacement in a portion of a conduit system. One method of making a repair is to shut down the entire system so that a portion may be repaired. This method is not desirable in many instances, whether it be an industrial system as in an oil refinery, or a commercial system, as in a municipal water system or a municipal gas distribution system.
There are a variety of means which allow repair, replacement, relocation or an installation of new parts into a pressurized conduit or piping system with no loss of service to the entire system, and minimal draining or bleeding of the fluid contents in a particular conduit. Conduit stopping or plugging is accomplished in virtually every type of piping material and in conduits conveying virtually every type of fluid.
Most mechanical stopping or blocking procedures require that a lateral access opening be made in the conduit to permit a stopper or block to be inserted into the conduit. The usual procedure to cut the access hole into the conduit is variously called hot tapping, wet tapping, pressure tapping, side tapping, and a variety of other terms depending upon the given industry and the locale.
Hot tapping involves mounting a nozzle onto the conduit with a pressure tight fit between the nozzle and the conduit. A gate-type valve is mounted on the nozzle and a pressure tight cutting machine is mounted on the valve. The valve is opened and a cutter from the cutting machine is advanced through the valve to engage the conduit to cut an access opening into the conduit. After the access opening is cut, the cutter is retracted outward through the valve. The valve is closed. Then, the cutting machine is removed without loss of pressure or flow in the conduit.
The size of the access opening in the conduit is determined by the design and size of the particular plug or stopper. In most instances, stoppers require an access hole having a diameter which is 95% or more of the interior diameter of the conduit. Certain stoppers require access openings which are as small as 70% or 80% of the size of the interior diameter of the conduit. It is desirable to have a smaller access opening because the structural integrity of the tapped conduit is inversely proportionate to the size of the access opening. In addition, various material and tooling costs are reduced when the size of the access opening is decreased.
The utilization of access holes for stopper devices which holes are less than 95% of the diameter of the conduit is disclosed in three U.S. Pat. Nos., namely; 3,120,246, issued Feb. 4, 1964, entitled, "Conduit Stopper", the inventor being Fritz Alter; 3,115,163, issued Dec. 24, 1963, entitled, "Means For Stopping The Flow Of Fluid In A Conduit", the inventors being, Kenneth S. Van Epps and Walter E. Magnus; and 2,272,734, issued Feb. 10, 1942, entitled, "Means For Stopping Flow Of Fluid In Conduits", the inventor being Irwin H. Witt. Each of the three patents teaches a flat generally rectangular resilient sealing element. Witt discloses a sealing element having an arcuate bottom portion for engagement with the interior of the conduit. Alter and Van Epps, each discloses a resilient carrier having a vertical slot to receive the flat sealing element and a retainer screw threaded to the carrier. In each of the three patents, the carrier is inserted into the pressurized conduit utilizing a hollow jack screw. When the carrier is positioned inside the conduit, a second jack screw inside the first jack screw advances the sealing element against the conduit forcing it to deform outward from the carrier into sealing contact with the inner wall of the pipe. The use of the double jack screw greatly increases manufacturing costs of the stopper because of the plurality of parts required and the precise tolerances needed for proper operation. In addition, more seals are needed to prevent leakage from the pressurized conduit through the machine and into the environment. The spatial limitations necessitate that certain parts are smaller, and thereby more fragile than would be desired in a machine for use in the field by the mechanical trades which perform the piping repair functions. Each of the three disclosures teaches a different method of sealing the outside of the carrier to the bore or nozzle. None utilizes a positive sealing system that compresses a resilient gasket against a metal seat.
In some instances, it is desirable to isolate a section of conduit but still keep the entire system operative. An accepted means is taught by the above identified U.S. Pat. No. 2,272,734, to Witt and U.S. Pat. No. 3,115,163, to Van Epps et al. Each of these patents teaches a similar arrangement. Two conduit stoppers are mounted on the conduit. Two additional nozzles and valves are mounted onto the conduit and then hot tapped to provide a connection into the conduit. A bypass pipe is then installed between the two valves, allowing flow to the system downstream of the stopper installation. Both Witt and Van Epps do not teach a bypass conduit that can be connected to their stopper apparatus. Therefore, the prior art requires the two extra hot taps be effected to provide the bypass.
The Mueller Co. of Decatur, Ill. discloses a bypass rubber stopper for use in a stopper for diversion of flow of a fluid. This disclosure is contained in pages J-3-2 and J-3-4 of Bulletin J-3 Line Stopping Unit No. 3 published May, 1977.